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Dinosaur extinction didnâ€™t usher in present-day mammals

A new, complete ‘tree of life’ tracing the history of all 4,500 mammals on Earth shows that they did not diversify as a result of the death of the dinosaurs, says new research published in Nature today.

The study was undertaken in the UK by scientists at Imperial College London and the Zoological Society of London (ZSL). It contradicts the previously accepted theory that the Mass Extinction Event (MEE) that wiped out the dinosaurs 65 million years ago prompted the rapid rise of the mammals we see on the earth today.

The multinational research team has been working for over a decade to compile the tree of life from existing fossil records and new molecular analyses. They show that many of the genetic ‘ancestors’ of the mammals we see around us today existed 85 million years ago, and survived the meteor impact that is thought to have killed the dinosaurs. However, throughout the Cretaceous epoch, when dinosaurs walked the earth, these mammal species were relatively few in number, and were prevented from diversifying and evolving in ecosystems dominated by dinosaurs.

The tree of life shows that after the MEE, certain mammals did experience a rapid period of diversification and evolution. However, most of these groups have since either died out completely, such as Andrewsarchus (an aggressive wolf-like cow), or declined in diversity, such as the group containing sloths and armadillos.

The researchers believe that our ‘ancestors’, and those of all other mammals on earth now, began to radiate around the time of a sudden increase in the temperature of the planet – ten million years after the death of the dinosaurs.

Professor Andy Purvis New Window from Imperial College London’s Division of Biology explains: “Our research has shown that for the first 10 or 15 million years after the dinosaurs were wiped out, present day mammals kept a very low profile, while these other types of mammals were running the show. It looks like a later bout of ‘global warming’ may have kick-started today’s diversity – not the death of the dinosaurs.

“This discovery rewrites our understanding of how we came to evolve on this planet, and the study as a whole gives a much clearer picture than ever before as to our place in nature.”

Dr Kate Jones from the Zoological Society of London adds: “Not only does this research show that the extinction of the dinosaurs did not cause the evolution of modern-day mammals, it also provides us with a wealth of other information. Vitally, scientists will be able to use the research to look into the future and identify species that will be at risk of extinction. The benefit to global conservation will be incalculable.”

The study was supported by the UK Natural Environment Research Council (NERC), the National Center for Ecological Analysis and Synthesis (NCEAS), the German Federal Ministry of Education and Research (BMBF), the German Research Association (DFG) Heisenberg, the Leverhulme Trust, the National Science Foundation (NSF), the Earth Institute at Columbia University, and the Cyberinfrastructure for Phylogenetic Research (CIPRES).